San Ildefonso is a small, peaceful coastal town located in the southern part of Ilocos Sur, nestled between the municipalities of Santa and Sinait. It’s part of the second district of the province and sits along the western coast of Luzon, facing the South China Sea (West Philippine Sea).
The town is primarily agricultural, with many residents engaged in farming, fishing, and handicrafts. Despite its small size, it reflects the rich Ilocano culture and traditions, with strong community ties and simple rural living.
San Ildefonso is one of the Ilocos Sur towns historically known for producing basi, alongside nearby areas like San Vicente and Vigan. The fertile farmlands of San Ildefonso are ideal for sugarcane cultivation, making it a natural center for basi-making.
The parish traces its roots to the Spanish colonial era.
It was initially a visita (mission chapel) of Bantay or Vigan during the 18th century, later becoming an independent parish around 1769–1906.
It was established under the advocacy of St. Ildephonsus, a 7th-century Archbishop of Toledo known for his devotion to the Blessed Virgin Mary.